Understanding Weed Barriers of Entry #TheAdjuvantSeries

The next part in our adjuvant series will discuss the different kinds of barriers that hold herbicides back from killing weeds. Weeds differ in their ability to be penetrated and some herbicides require certain adjuvants to assist. Without an adjuvant, some herbicides may only have a 3% absorption rate through the barriers. These barriers include: leaf angle, leaf hairs, leaf surface and the cell wall.

Barriers of Entry

Leaf Angle:
• Grasses have a smaller target area to cover vs. broadleaf weeds
• Downward or upward leaf angles present challenges for the herbicide to hit its mark
*A guar based adjuvant will aid in the leaf angle barrier by the polymer’s unique retention.

Leaf Hairs:
• Extremely hairy leaves will hold spray droplets away from the leaf surface
• The hair patterns will cover the leaf and repel water
• Prevents a solid leaf and spray contact
*Oil based adjuvants and surfactants decrease the surface tension of the droplet, which allow it to meet the leaf.  

Leaf Surface (cuticle):
• The waxes on the leaf surface are nonpolar and oil like which forms an effective water repellent layer
• The hydrophobic coatings of weed surfaces (epicuticular wax) will have to be broke through to enable pesticide penetration
*Adjuvants that can solubilize thick waxy leaf cuticles (hardened weeds) will allow the herbicide to access the plant sooner.

Cell Wall:
• The cell wall is sometimes filled with water and will have little resistance to water soluble herbicides
*Adjuvants can help low-water soluble herbicides penetrate the region.

The amount that adjuvants assist in proper herbicide penetration cannot go unnoticed. Broadening knowledge on adjuvant selection will help in choosing the right one for the job. At Novus Ag, we carry a strong line of adjuvants and would love to get you the right one for your post-emergence applications. Next week, we will discuss where adjuvants came from and the different kinds. That way you can have a better understanding of what you are mixing in your tank.

References:

Rosen’s Inc. Medallion Quality Adjuvant Guide

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